[peasleer]

I want to build an external power supply (I was thinking with a TREAD) for current use with my CMoy, and for use with other amps in the future. It would be housed in a separate enclosure. Is this stupid?

I don't even know how I would hook it up to the amps I would want to power: my thought was to have a socket on the enclosure and a regular DC jack on the amps, then make a cable for the socket to the jack, but I have no idea if there is a better way to do it or if I should just build a separate PSU for each future amp, and just use a standard wall wart for the CMoy.

So yeah. Feel free to point out all the reasons why this would or wouldn't work and any alternate suggestions you all may have

 

[heatmizer]

That sound like a very nice way for a power supply.
Alot of the high end stuff use a remote power supply.

 

[ericj]

It depends how much power you expect to need for future amps.

you can get a fairly small 24v or 30v flat-pack transformer of about VA size 6 and cram it into a jameco wall-wart enclosure with a tread or similar, but that's only like 200ma, which would be enough for a pimeta but not for a bigger amp.

 

[tomb]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif It depends how much power you expect to need for future amps. you can get a fairly small 24v or 30v flat-pack transformer of about VA size 6 and cram it into a jameco wall-wart enclosure with a tread or similar, but that's only like 200ma, which would be enough for a pimeta but not for a bigger amp.

Actually, you can cram a 800ma, 24V transformer into a Jameco walwart enclosure, and still leave room for an upsized cap (1000uF, 63V). The next one will have four of those caps, I hope.

 

[peasleer]

Is this the enclosure you used, tomb?

http://tinyurl.com/3ycwrf

If a TREAD will fit in that, then that looks like a pretty awesome solution. I guess if I ever decide to build and amp requiring more power than a pimeta I'll probably be in a better position to build a better power supply anyway

 

[tomb]

Quote:

Originally Posted by peasleer /img/forum/go_quote.gif Is this the enclosure you used, tomb? http://tinyurl.com/3ycwrf If a TREAD will fit in that, then that looks like a pretty awesome solution. I guess if I ever decide to build and amp requiring more power than a pimeta I'll probably be in a better position to build a better power supply anyway

Yep - that's it. The xfmr is a dual secondary split-bobbin rated for 48V at 400ma, or 24V at 800ma - only $2.59, also at Jameco. The inline fuse holder is a 5x20 that's only $0.67, again at Jameco.

The TREAD is mounted upside down with a small hole cut in the bottom for adjusting the trimmer. The cap is mounted on the underside of the board, which puts it on the top in this arrangement. The LM317 is also mounted on the bottom of the board, with some extra length leads. This allows the regulator to be fed through a hole out the back, where it is mounted on the outside with a heat sink.

It was a bit of work figuring it all out, but the whole package is super convenient. It's relatively small, can be carried, and plugs into anything - wall or amp.

 

[balou]

peasleer - if you're building a psu, I'd recommend making a dual supply. this way, you won't have to worry anymore about virtual ground circuits, their max output power and their stability

 

[peasleer]

Oi man, you are making me work!

Just checking, is this the transformer?
http://tinyurl.com/32f8uw

And the fuse holder?
http://tinyurl.com/396otj

I'm new to electronics and DIY. Is there a thread/page that outlines this setup with more detail? If not, this seems like a bit of a challenge - but something I'm wanting to do.

So the part that plugs into the wall is mounted internally somehow to the fuse holder (it looks like it just slides on?), and the output from that goes into the transformer which lowers the wall voltage to something the TREAD can handle, which then regulates the power. Close? I'd love to see the back of your modified enclosure if possible - I didn't quite follow how you hooked things up externally.

Thanks for your help

 

[peasleer]

Quote:

Originally Posted by balou /img/forum/go_quote.gif peasleer - if you're building a psu, I'd recommend making a dual supply. this way, you won't have to worry anymore about virtual ground circuits, their max output power and their stability

Good points.

I guess now the decision is between a bigger PSU better able to handle future projects, or something tidy that will work for now. I see the advantages of both.

I'm leaning toward a dual supply, but I'll need help constructing either

 

[balou]

yes and yes.
the fuse just comes in between one wire going to the transformer

for a dual supply, you basically need a transformer with two secondaries, that means one with two 12v output instead of one 24v. or alternatively, 2 12v transformers.
then you need two regulator circuits, one for each output. in the end, you connect the + of one regulator to the - of the other one, which will leave you with three outputs: -, +/-, +. the +/- becomes your ground

it's described on tangents site: http://tangentsoft.net/elec/tread/pguide.html#dual
it contains the regulator circuit, pcb layout, how to wire it to a dual system, and basically everything else you need to start with audio DIY (tangents site was the single most useful resource for me when I started with DIY)

do you like soldering really tiny smd components? then I'd have a all-in-one board up my sleeve. but as I already said... reeeeally tiny, I wonder if I'll be able to solder it...


edit: seems like I was a little bit slow

 

[tomb]

Quote:

Originally Posted by peasleer /img/forum/go_quote.gif Oi man, you are making me work! Just checking, is this the transformer? http://tinyurl.com/32f8uw And the fuse holder? http://tinyurl.com/396otj

Yep - right on both counts!

Quote:

I'm new to electronics and DIY. Is there a thread/page that outlines this setup with more detail? If not, this seems like a bit of a challenge - but something I'm wanting to do.

Yes, you are correct that it's a bit of a challenge. I've been intending to do some how-to-do-it pages, but the MAX and its website got in the way lately.

To tell the truth, I recently made a couple of dongles with TREADS in the smallest Radio Shack project box. It's simply spliced into the leads about six inches from a standard 24VAC, 500ma walwart. After doing that, though, I decided that the one above was less work, more powerful, and easier to use.

Quote:

So the part that plugs into the wall is mounted internally somehow to the fuse holder (it looks like it just slides on?), and the output from that goes into the transformer which lowers the wall voltage to something the TREAD can handle, which then regulates the power. Close? I'd love to see the back of your modified enclosure if possible - I didn't quite follow how you hooked things up externally. Thanks for your help

There is no external hookup. The smaller half of the walwart enclosure has two plug blades and a ground rod that stick through to the inside of the case. There are two 90 degree push-on type blade connectors connected to the blades (I ignored the ground). One has a lead that goes to one of the transformer primaries, the other goes to the inline fuse holder which then goes to the other transformer primary. This is what forms the 110/120V side.

The secondaries are wired together in parallel (to get 24VAC @ 800ma) and then connected to the input of the TREAD. The output leads come ready-made with a 2.1mm connector from Mouser. They are connected to the + and - DC outputs of the TREAD and routed through the walwart strain relief, providing the TREAD-regulated DC output, with voltage adjustable from the trimmer screw accessible from the bottom.

For all intents and purposes - except for a few more screws sticking out - it looks just like any other walwart.

 

[peasleer]

Quote:

Originally Posted by balou /img/forum/go_quote.gif for a dual supply, you basically need a transformer with two secondaries, that means one with two 12v output instead of one 24v. or alternatively, 2 12v transformers.

Great, I'm actually starting to understand this! Still, I looked on jameco for a dual secondary transformer, but couldn't find one. Would you mind helping me out with this? Otherwise, best guess for a single 12v transformer: http://tinyurl.com/yt85fw

Quote:

Originally Posted by balou /img/forum/go_quote.gif then you need two regulator circuits, one for each output. in the end, you connect the + of one regulator to the - of the other one, which will leave you with three outputs: -, +/-, +. the +/- becomes your ground

Alright, I think this all makes sense. Wall AC in going to two transformers, + and - out from one transformer goes to + and - in of one TREAD, repeat for the second transformer and TREAD, then solder one wire out of the first TREAD for -, one out of the second TREAD for +, then one wire connecting the + of the first TREAD and - of the second together to make +/- ground. Sound right for two single transformer layout? I also believe I understand how I would do this for a dual secondary transformer, the only change would be in how I wired the AC in as mentioned on tangent's site.

I'm a little concerned about exposing myself to wall power for this. Any tips for safety and confidence?

Quote:

Originally Posted by balou /img/forum/go_quote.gif do you like soldering really tiny smd components?

Haha, I have enough trouble not bridging leads as it is

I'll stick with the "basic" dual supply for now

I'm at work now, but soon I'm going to start gathering a parts list and putting together the steps I'll need to build an external dual power supply. Afterward, I'll put up the parts list and instructions (with pictures) up for others to follow. Hopefully it will be helpful to someone else!

 

[peasleer]

Oh, duh! I just re-read tomb's post and realized the original transformer he had referred me to was a dual-secondary type. Ignore the request for help in finding two single secondary transformers

Alrighty then, I'm feeling more confident with the assembly of this supply. Tonight I'll make my parts list for the power supply and post it for review.

 

[ericj]

For myself, I'm actually more interested in building a fully filtered AC power brick. Generally requires an enclosure much larger than Jameco sells, unfortunately.

I built a 2.75 amp 36vac brick for my M3, with full steps-alike AC filter stage, into the carcass of a circa 1980 9vdc 2a switching power brick. I'm working on an LM338K based regulator board to go in the same enclosure as the M3, but futurlec hasn't delivered my TO-3 heatsink yet.

With the Millett Max boards imminent, I'd like to build a similar 30vac brick.

Anybody know where i can get a plastic enclosure big enough for the AC filter stage and a 30vac 1A trafo? Maybe I'll just have to gut another old power brick.

 

[peasleer]

Whoops, I goofed.

Right now I'm thinking of using a standard three-prong AC plug from wall to the enclosure so everything will be handled internally. From there, I'll have a slow-burn fuse before connecting to the transformer. Before I was reasonably certain that this transformer was dual-secondary:

http://tinyurl.com/32f8uw

But from what I understand of the datasheet, it is alluding to having potentially dual *primaries,* and not mentioning anything about dual secondaries.

Can anyone let me know definitively if it is or isn't? And if it isn't, point me in the right direction? Parts selection is going well otherwise